Nonzero orbital moment in high coercivity ε-Fe2O3 and low-temperature collapse of the magnetocrystalline anisotropy

The magnetic properties of epsilon-Fe2O3 nanoparticles are investigated by x-ray magnetic circular dichroism. Sum rules relating the orbital and spin moment in the Fe 3d band to the Fe L-2,L-3 absorption cross sections show that the Fe orbital moment (m(orb)) is considerably high, explaining the origin of the large coercivity of this material at room temperature. Moreover, at T similar to 110 K, the collapse of the coercivity (H-c) and the magnetocrystalline anisotropy coincides with a strong reduction of the spin-orbit coupling evidenced by a drastic drop of m(orb). The decrease in m(orb) originates from changes in the electron transfer between Fe and O ions accompanied by significant modifications of some of the Fe-O bond distances. Similarly, the recovery of m(orb) at lower temperatures mimics the behavior of the Fe-O bond lengths.